Haskell 选择判断语句要写一个语句,写在.hs文件里面,然后GHCi调用,就是算一个数的hailstone 值这是

mintfantasy2022-10-04 11:39:541条回答

Haskell 选择判断语句
要写一个语句,写在.hs文件里面,然后GHCi调用,就是算一个数的hailstone 值
这是我写的hs文,想表达一个算式,“如果n为偶数,得出它的一半值,如果为奇数,算三倍n加1”
hailstone n
| rem n 2 = 0 = n/2
| otherwise = 3n+1
但是GHCi一直提示读取错误,在我用:l xxxx.hs 读取时,
显示第二行的第一个等号有错误
请求指导

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草棚棚共回答了20个问题 | 采纳率95%: 问题出再你用了=而不是==
不过这个条件你完全可以直接用even n, 而不必写成rem n 2 == 0; 1年前

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matches a [] = []
matches a (x:xs) = if a == x then x:matches a xs else matches a xs
类型必须是Eq的实例,不然==无法判断,至少例子上的整数和字符都是的,大部分常见的类型也都是Eq的实例

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splits xs = sp ((length xs)-1) xs
sp 1 xs = [splitAt 1 xs]
sp n xs = (sp (n-1) xs) ++ [splitAt n xs]
```
第二道题copy自[stackoverflow](http://stackoverflow.com/a/21722065/2214113)
```haskell
commonPrefix :: (Eq e) => [e] -> [e] -> [e]
commonPrefix _ [] = []
commonPrefix [] _ = []
commonPrefix (x:xs) (y:ys)
| x == y = x : commonPrefix xs ys
| otherwise = []
cpfx :: (Eq a) => [[a]] -> [a]
cpfx = foldl1 commonPrefix
```
该睡了,后面两个改天有时间再说,我才不告诉你我不会.

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